Tim the tool man

My KXR has 95 k on the clock. It has a persistent oil leak coming from the transfer case extension housing seal. I have replaced the seal 3 times with the last time including a speedy seal on the tail shaft yoke. Still leaking... I am now thinking a breather problem but I cant locate it. Are there any ideas out there.? The yoke has the tiniest impression from the seal . The yoke is not a serviceable part from Toyota. The complete shaft $2700. OUCH!!!!!! Is anyone else had this problem??